#!/usr/bin/env python3

class Account(object):
	def __init__(self, rate):
		self.__amt = 0
		self.rate = rate

	@property
	def amount(self):
		return self.__amt

	@property
	def cny(self):
		return self.__amt * self.rate

	@amount.setter
    def amount(self, value):
		if value < 0:
			print("Sorry, no negative amount in the account.")
			return
        self.__amt = value

if __name__ == '__main__':
	acc = Account(rate=6.6)
	acc.amount = 20
	print("Dollar amount:", acc.amount)
	print("In CNY:", acc.cny)
	acc.amount = -100
 	print("Dollar amount:", acc.amount)
